In an FAQ on the Doom site, Bethesda said beta access will come through an insert inside boxed copies of Wolfenstein: The New Order. Redeeming its key code entitles the user to participate int he Doom beta "once it begins." No other details as far as timing, duration or platform options for the Doom beta were given.

Oh yeah, Bethesda also released this trailer—of Wolfenstein, mind you, not Doom.